----- Message d'origine -----De: "Ross S. W. Walker" <[EMAIL PROTECTED]>Date: Mardi, Novembre 13, 2007 9:12 amObjet: Re: [CentOS] Need advice on storageÀ: centos@centos.org> > If you are seeing iowaits that high then something needs to be done.> > You CAN gain performance by striping, but the downtime due to > disk failure can make your decision making skills look flawed.> > For a mail server I highly recommend RAID10 and drives with high > RPM so you get better random io performance as 99% of io on a > mail home server will be random io and while regular SATA drives > would be ok for a file server which is mostly sequential they > will stack up io waits on a busy mail or database server. The > raptors are costly because they run at 10k rpm and have low seek > times, this gives them much better random io performance, but > sequential io is the same with regular SATA drives. In fact > sequential io performance is almost identical between 7200rpm > SATA and 15000rpm SAS the real difference is in random io where > the 15k drives are 2x faster (1.2MB of 4k random ios a second > versus 640KB of 4k random ios a second, unbuffered).> > If you have an external enclosure then that will help, but make > sure the array is compatible with the drives you want. SATA > disks cannot go into a SCSI array, though some SAS enclosures > and controllers allow you to mix SAS and SATA drives (LSI is one).> > Performance can trump size here so if the choice is between > 200GB 7200 rpm SATA drives or 72GB 15000rpm SAS drives, if your > data fits onto the 72GB drives (probably 140GB if in a 4 drive > RAID10) go with the 72GB drives (taking growth into > consideration too).> > Hardware RAID can help too if you utilize onboard battery backed > up write-back cache. The more write-back cache the better, just > make sure it is battery backed up (BBU).> > -Ross> Hi Ross, Good technical explanation. I'm finally planning to go RAID 10 on a VTrak 15100 (It has battery backup). As i said in another post, i found the VTrak to have a free SCSI bus and free SATA slots. This unit has 2 independant SCSI buses and uses SATA drives. It remains to be seen if the controller is non blocking when using 2 servers. When we'll have the budget to replace the server, i'll probably go with something like a Tyan TA26 (S3992 ServerWorks chipset) with SAS 15K Drives and Adaptec 3405 if CentOS has good support for it. Communigate stores messages in mbox files so we have a lot of them (about 40-45 users with a huge Public folders holding all our projects infos). The actual dataset is about 65 Gigs (and growing!). So the random seek is important.Thanks for your comment!Guy Boisvert
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